TL074 datasheet(21/39 Pages) TI2

21 / 39 page

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

-50

-25

100

125

T ( C)

J °

MaxI

(dc)

MaxI

(RMS)

OUT

MAXIMUMOUTPUTCURRENTvsJUNCTIONTEMPERATURE

OPA564

www.ti.com

SBOS372E

– OCTOBER 2008 – REVISED JANUARY 2011

CURRENT LIMIT FLAG

Depending on load and signal conditions, the thermal

protection circuit may cycle on and off. This cycling

The OPA564 features a current limit flag (IFLAG) that

limits

the

amplifier

dissipation,

but

may

have

can be monitored to determine if the load current is

undesirable effects on the load. Any tendency to

operating within or exceeding the current limit set by

activate

the

thermal

protection

circuit

indicates

the user. The output signal of IFLAG is compatible with

excessive

power

dissipation

inadequate

standard CMOS logic and is referenced to the

heatsink.

For

reliable,

long-term,

continuous

negative supply pin (V

–). A voltage level of + 0.8V or

operation, with IOUT at the maximum output of 1.5A,

less with respect to V

– indicates that the amplifier is

the junction temperature should be limited to +85

°C

operating within the limits set by the user. A voltage

maximum. Figure 44 shows the maximum output

level of +2.0V or greater with respect to V

– indicates

current versus junction temperature for dc and RMS

that the OPA564 is operating above (exceeds) the

signal outputs. To estimate the margin of safety in a

current limit set by the user. See Setting the Current

complete design (including heatsink), increase the

Limit for proper current limit operation.

ambient temperature until the thermal protection

triggers.

Use

worst-case

and

signal

OUTPUT STAGE COMPENSATION

conditions. For good, long-term reliability, thermal

protection should trigger more than 35

°C above the

The complex load impedances common in power op

maximum

expected

ambient

condition

the

amp applications can cause output stage instability.

application.

For normal operation, output compensation circuitry is

typically not required. However, if the OPA564 is

The internal protection circuitry of the OPA564 was

intended to be driven into current limit, an R/C

designed to protect against overload conditions; it

network (snubber) may be required. A snubber circuit

was not intended to replace proper heatsinking.

such as the one shown in Figure 54 may also

Continuously

running

the

OPA564

into

thermal

enhance stability when driving large capacitive loads

shutdown degrades reliability.

(greater

than

1000pF)

inductive

loads

(for

example,

motors

loads

separated

from

the

amplifier by long cables). Typically, 3

Ω to 10Ω in

series with 0.01mF to 0.1mF is adequate. Some

variations in circuit value may be required with certain

loads.

OUTPUT PROTECTION

The output structure of the OPA564 includes ESD

diodes (see Figure 43). Voltage at the OPA564

output must not be allowed to go more than 0.4V

beyond either supply rail to avoid damaging the

device.

Reactive

and

electromagnetic

field

(EMF)-generation loads can return load current to the

amplifier, causing the output voltage to exceed the

power-supply voltage. This damaging condition can

be avoided with clamping diodes from the output

terminal to the power supplies, as Figure 54 and

Figure 44. Maximum Output Current vs Junction

Figure 55 illustrate. Schottky rectifier diodes with a 3A

Temperature

or greater continuous rating are recommended.

THERMAL PROTECTION

USING TSENSE FOR MEASURING JUNCTION

The OPA564 has thermal sensing circuitry that helps

TEMPERATURE

protect the amplifier from exceeding temperature

The OPA564 includes an internal diode for junction

limits. Power dissipated in the OPA564 causes the

temperature monitoring. The h-factor of this diode is

junction

temperature

rise.

Internal

thermal

1.033. Measuring the OPA564 junction temperature

shutdown circuitry disables the output when the die

can be accomplished by connecting the TSENSE pin to

temperature

reaches

the

thermal

shutdown

a remote-junction temperature sensor, such as the

temperature limit. The OPA564 output remains shut

TMP411 (see Figure 57).

down until the die has cooled sufficiently; see the

Electrical Characteristics, Thermal Shutdown section.

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